Since the outset of the Industrial Revolution in the late 1700s, the portion of the earth's atmosphere that is comprised of carbon dioxide increased from about 0.03% to 0.04%. More precisely, CO2 in 1744 was 0.0277%, and it is now 0.0412%, a relative increase of 49%. As documented in various scientific sources, carbon dioxide is: (1) "colorless, odorless," and "non-toxic" at atmospheric levels, (2) "required for the photosynthesis of all plants," (3) "vital to life" because "almost all biochemicals found within living creatures derive directly or indirectly from" it, and (4) "contributes more" to the greenhouse effect than "any other gas" released by human activity. Adding CO2 to the earth's atmosphere tends to increase its temperature, but this doesn't cause a "runaway greenhouse effect" because the capacity of CO2 to absorb more heat stagnates with increasing concentrations.